In a way you are correct. I am not going to debate (much) exactly what the power source is out of the magnetos in the stator/flywheel but......
To be AC you have to have a return and that is not present. IE: The neutral wire in your house wiring.
The Puch has a "pulsed" voltage source of + 6V and chassis ground. That's it. And Puch 7-wire "may" have 4 sources which will mean I have two that are 180 degrees out of phase so I should be able to rectify and produce DC. After cleaning it up with a good capacitor that is.
So, if I leave the coil feed alone and only mess with the lights I should be able to do this but we'll see. hmmm....6v one side, 6v the other. With some capacitors and a voltage regulator I could convert to 12v for the lights if the output is enough to produce a charge.